In document copiers it is often desirable to afford the user the option of using more than one size copy paper. For example, it is customary in the U.S. to use 11-inch copy paper for most purposes but 14-inch copy paper is used to record legal size documents. Similarly, in other countries it is frequently desirable to provide the opportunity for the user to copy on more than one size paper.
In an optics system which magnifies or reduces the size of the document being copied, and wherein a scanning optical system is used, the scanning mechanism must travel, for example, 14 inches in order to copy a legal size document. If the copy is recorded onto legal size copy paper, the result is a 1:1 copy. To achieve reduction in such a system, the scanning velocity must be increased relative to the velocity of the copy paper (photoreceptive surface). To accomplish this with a drive which uses a mechanical velocity-multiplying scheme for reduction, the length of scan travel increases with an increase in scan velocity. Thus, if the machine is to achieve, for example, 0.647 reduction, the length of scan would be 14/0.647 or 21.64 inches long. Note however, that if 11-inch copy paper were in use, despite the 21.64-inch length of the scan, 0.647 reduction could accomodate paper of only 17-inch size and still place the entire document on the 11-inch copy paper. Therefore, the length of scan is much longer (21.64 inches) than the usable length of the document glass (17 inches). This not only means wasted space, but also means the size of the machine is larger than necessary.
The prior art shows U.S. Pat. No. 3,897,148 to Ritchie et al (IBM) which utilizes three cams, one of which is selected to provide a differing scan length and speed for the illumination carriage of a three-position reduction document copier machine. The system therein is directed to an optics system which has three discrete magnification ratios and is not directed to a system in which the magnification ratio is continuously variable between boundaries. Therefore, it is an object of this invention to provide a continuously variable reduction system in which it is possible to copy a plurality of documents at a 1:1 magnification ratio on various size copy paper and to provide continuously variable reduction of documents on a machine where the document glass size (or scan length) is not any larger than the largest size document to be reduced.